In order to improve the performance of a golf club, golf club designers have constantly struggled with finding different ways to hit a golf ball longer and straighter. Designing a golf club that hits a golf ball longer may generally require an improvement in the ability of the golf club head to effectively transfer the energy generated by the golfer onto a golf ball via the golf club. Hitting a golf ball straighter, on the other hand, will generally require an improvement in the ability of the golf club to keep the golf ball on a relatively straight path even if the golf ball is struck off-center; as a golf ball that is struck at the center of the golf club head will generally maintain a relatively straight flight path.
Effectively transferring the energy generated by the golfer onto a golf ball in order to hit a golf ball further may be largely related to the Coefficient of Restitution (COR) between the golf club and the golf ball. The COR between a golf club and a golf ball may generally relate to a fractional value representing the ratio of velocities of the objects before and after they impact each other. U.S. Pat. No. 7,281,994 to De Shiell et al. provides one good example that explains this COR concept by discussing how a golf club head utilizing a thinner striking face may deflect more when impacting a golf ball to result in a higher COR; which results in greater travel distance.
Being able to hit a golf ball relatively straight even when the club strikes a golf ball at a location that is offset from the center of the striking face may generally involve the ability of the golf club to resist rotational twisting; a phenomenon that occurs naturally during off-center hits. U.S. Pat. No. 5,058,895 to Igarashi goes into more detail on this concept by discussing the advantages of creating a golf club with a higher Moment of Inertia (MOI), which is a way to quantify the ability of a golf club to resist rotational twisting when it strikes a golf ball at a location that is offset from the geometric center of the golf club head. More specifically, U.S. Pat. No. 5,058,895 to Igarashi utilizes weights at the rear toe, rear center, and real heel portion of the golf club head as one of the ways to increase the MOI of the golf club head, which in turn allows the golf club to hit a golf ball straighter. It should be noted that although the additional weights around the rear perimeter of the golf club head may increase the MOI of the golf club, these weights can not be added freely without concern for the overall weight of the golf club head. Because it may be undesirable to add to the overall weight of the golf club head, adding weight to the rear portion of the golf club head will generally require that same amount of weight to be eliminated from other areas of the golf club head.
Based on the two above examples, it can be seen that removing weight from the striking face of the golf club head not only allows the golf club head to have a thinner face with a higher COR, the weight removed can be placed at a more optimal location to increase the MOI of the golf club head. One of the earlier attempts to remove unnecessary weight from the striking face of a golf club can be seen in U.S. Pat. No. 5,163,682 to Schmidt et al. wherein the striking face of a golf club head has a variable thickness by making the part of the striking face that is not subjected to the direct impact thinner.
U.S. Pat. No. 5,425,538 to Vincent et al. shows an alternative way to remove unnecessary weight from the striking face of a golf club by utilizing a fiber-based composite material. Because fiber-based composite materials may generally have a density that is less than the density of traditional metals such as steel or titanium, the simple substitute of this fiber-based composite material alone will generate a significant amount of discretionary weight that can be used to improve the MOI of a golf club. Fiber-based composite materials, because of their relatively lightweight characteristics, tend to be desirable removing weight from various portions of the golf club head. However, because the durability of such a lightweight fiber-based composite material can be inferior compared to a metallic type material, completely replacing the striking face of a golf club with the lightweight fiber-based composite material could sacrifice the durability of the golf club head.
U.S. Pat. No. 7,628,712 to Chao et al. discloses one way to improve the durability of striking face made out of a fiber-based composite material by using a metallic cap to encompass the fiber-based composite material used to construct the striking plate of the golf club head. The metallic cap aids in resisting wear of the striking face that results from repeated impacts with a golf ball, while the rim around the side edges of the metallic ring further protects the composite from peeling and delaminating. The utilization of a metallic cap, although helps improve the durability of the striking face of the golf club head, may not be a viable solution, as severe impact could dislodge the fiber-based composite from the cap.
In addition to the durability concerns of the fiber resin matrix itself, utilizing composite materials to form the striking face of a golf club offers additional challenges. More specifically, one of the major design hurdles arises when a designer attempts to bond a fiber-based composite material to a metallic material, especially at a location that is subjected to high stress levels normally generated when a golf club hits a golf ball. Finally, the usage of composite type materials to form the striking face portion of the golf club head may also be undesirable because it alters the sound and feel of a golf club away from what a golfer are accustomed to, deterring a golfer from such a product.
Ultimately, despite all of the attempt to improve the performance of a golf club head by experimenting with alternative face materials, the prior art lacks a way to create a striking face that saves weight, improves COR, and is sufficiently durable without sacrificing the sound and feel of the golf club head. Hence, as it can be seen from above, there is a need in the field for a golf club head having a striking face that can save weight, improve the COR of the golf club head, and can endure the high stress levels created by the impact with a golf ball, all without sacrificing the sound and feel of the golf club head.